Hello glyn_griffiths
A Cylindrical Support constrains radial motion while allowing rotational and axial motion on a selected cylindrical face while a Planar Support constrains motion normal to the surface on a selected face.
In this case, I would recommend using Cylindrical support at both ends.
While applying the cylindrical support, you may need to apply it individually to both ends. 
Please let me know if you face any issue with that.
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